The left-back has missed the entire season so far through injury, but made a comeback for the Saints' development side in midweek.
His performance in that game was impressive enough to convince Koeman that he is almost back up to speed, and the Dutch manager says that Bertrand will be included in the 18-man squad to face the Dons tonight.
“Very good, a long time out, it’s also difficult because he was out from May and that means no pre-season and a pre-season for a player is a very important part of the season for the player to be in a really good fit, physical stage,” Koeman said.
“We know that but little by little he will come back as he gets his time to play, that was good that he got 45 minutes on Monday and he will be part of the squad this Wednesday.”
Bertrand is one of Southampton's key players, and they have missed the qualities that he brings to the side in his absence.
Although the Saints have worked hard to bring in quality to cover for the England international, they do not have any other left-back of his class in their squad.
Bertrand is capable going forward, and he is stable defensively, meaning that he plays a key role in the attacking system that Koeman has devised at St. Mary's.
With Bertrand returning, Southampton will hope that he can kick-start their season, as they have not started the campaign particularly impressively.
Koeman's side are currently stationed in 16th position in the Premier League table, and they have just one league win to their name from their first six fixtures.